The present invention relates to heat-curable, chlorine- or bromine-containing halopolymer compositions containing a 1,3-diaminopropane curing agent, a sulfur source, and an acid acceptor and, more particularly, to a synergistic prevulcanization inhibitor therefor.
Chlorine- or bromine-containing halopolymers, such as the chlorinated polymers of ethylene, are well known materials which serve in many useful applications in commerce. These materials, which can be readily prepared, for example, by the polymerization of halogen-containing monomers or by post-halogenation of an olefinic polymer, possess a wide diversity of characteristics depending on several factors such as the structure, molecular weight, and nature of the halopolymer and the amount and distribution of the halogen moieties. Certain chlorine or bromine-containing halopolymers, particularly the high molecular weight chlorinated ethylene polymers, possess properties such that they can be cured to form highly useful, low cost elastomeric products.
Several methods for "curing" (or, alternatively, "vulcanizing" or "crosslinking") such halopolymers are known in the art. Chlorinated polyethylenes, for example, can be cured by reacting at elevated temperatures, a mixture of the desired polymer with organic peroxides, polyfunctional amines, aliphatic polyazo compounds, or a combination of sulfur, a Group II metal oxide, and a rubber vulcanization accelerator. Among these, the reaction with an organic peroxide has attained a prominent position in commercial processes for heat-curing chlorinated polyethylenes due to the high degree of cure achieved thereby.
In a copending U.S. patent application Ser. No. 945,944, filed Sept. 26, 1978, now U.S. Pat. No. 4,204,048, there is disclosed a process for making elastomeric materials by heat-curing a mixture of a chlorine- or bromine-containing halopolymer such as a chlorinated polyethylene, a 1,3-diaminopropane or salt thereof, a sulfur source and an acid acceptor. While the elastomers produced by that method are highly useful and much less expensive than the conventional peroxide-cured elastomers, the starting heat-curable mixtures were found to exhibit premature vulcanization both at room temperature and at elevated processing temperatures. Such premature vulcanization at room temperature (which results in an increase in the viscosity of the heat-curable mixture over time and, accordingly, reduces the shelf-life thereof) and at elevated temperatures (which is manifested by a decrease in scorch safety during processing) would typically be considered disadvantageous by commercial users.
Accordingly, it is an object of the present invention to provide a heat-curable chlorine- or bromine-containing halopolymer composition similar to that described in the aforementioned U.S. patent application, but having improved shelf-life and processing scorch safety.